The present invention relates to antennas, and more particularly to planar inverted-F antennas.
Antennas are widely utilized in automotive applications. In addition to the familiar AM/FM whip antenna, automobiles are increasingly equipped with antennas for GPS (Global Positioning System) and satellite radio. Typical frequencies for GPS antennas include 1.574 GHz to 1.576 GHz, while typical frequencies for satellite radio antennas include 2.320 GHz to 2.345 GHz. These antennas can be integrated into a single assembly contained within the vehicle or a housing typically mounted on the vehicle roof.
With the recent introduction of the Long Term Evolution (LTE) Advanced standard, antennas adapted for 4G communications must cover frequencies outside the frequency ranges for AM/FM, GPS and satellite radio. For example, LTE-compatible antennas must generally include a bandwidth covering a frequency range from 0.7 GHz to 2.7 GHz. In addition, shipping restrictions in the automobile industry limit the height of an antenna, including the housing, to 40 mm (millimeters) above the roof. Therefore, LTE-compatible automobile antennas must cover the frequency range for LTE communications—and in many instances existing GPS and satellite radio communications—while also maintaining a vertical profile of no more than 40 mm.
Existing antenna systems are incapable of meeting these requirements. For example, wideband monopole antennas are not capable of covering the desired frequency range. In addition, wideband monopole antennas do not currently meet a 40 mm height limitation.
Planar Inverted-F Antennas (PIFAs) are much lower in profile and meet the 40 mm height requirement. However, PIFAs do not meet bandwidth requirements for LTE communications. Current PIFAs have a bandwidth of approximately 10%, providing for example a frequency range of only 80 MHz for a center frequency of 800 MHz. In some instances the PIFA includes a dual resonating structure to improve the antenna's bandwidth. For example, a dual resonating structure can provide a second frequency centered at 1.9 GHz and covering the frequency range between 1.82 GHz and 1.98 GHz, marginally improving the total bandwidth to only about 240 MHz.